Such a motor controller for suppressing mechanical resonance has hitherto been disclosed, for example, in Patent Document 1.
In the following, a conventional motor controller is described with reference to FIG. 9. FIG. 9 is a block diagram of a conventional motor controller.
This conventional motor controller 90 is connected to motor 11 and speed detector 13. Motor 11 is connected with load 12. Further, speed detector 13 measures a speed of motor 11, and outputs speed detection signal Va indicating the speed of motor 11 based upon a result of the measurement.
Further, as shown in FIG. 9, motor controller 90 is provided with a plurality of serially connected notch filters 95a, 95b and 95c for a purpose of suppressing an oscillation caused by mechanical resonance. Moreover, motor controller 90 is provided with speed controlling section 94, frequency estimating section 97, notch filter selecting section 98, notch frequency setting section 99, and torque controlling section 96.
Frequency estimating section 97 estimates an oscillation frequency when an oscillation caused by mechanical resonance occurs. Notch filter selecting section 98 selects one notch filter out of notch filters 95a, 95b and 95c based upon a frequency estimated by frequency estimating section 97, and an enable or disable set state and a set notch frequency of each notch filter. Notch frequency setting section 99 sets the notch frequency of the one notch filter selected by notch filter selecting section 98 to the frequency estimated by frequency estimating section 97.
Further, speed controlling section 94 receives inputs of speed command signal Vt and speed detection signal Va, to generate torque command signal T1. Torque command signal T1 is supplied to notch filter 95a, and torque command signal T2 as a signal subjected to a filter process by notch filters 95a, 95b and 95c is supplied to torque controlling section 96. Torque controlling section 96 controls motor 11 based upon torque command signal T2 such that motor 11 outputs a target torque.
In conventional motor controller 90 configured in this manner, when an oscillation caused by mechanical resonance occurs, one appropriate notch filter is selected out of the plurality of notch filters based upon an estimated oscillation frequency, and an enable or disable set state and a notch frequency of each notch filter, and the notch frequency is reset. Since conventional motor controller 90 is provided with the plurality of notch filters, even when a plurality of mechanical resonances occur, the controller can respectively suppress oscillations caused by the respective mechanical resonance appropriately.
However, the conventional motor controller as described above has been configured to select one appropriate notch filter out of a plurality of notch filters based upon an oscillation frequency estimated in one frequency estimating section. For this reason, in a case of mechanical resonance being such an oscillation as to contain a plurality of frequency components, correct oscillation frequencies cannot be estimated, or a suppressing operation is performed only on one frequency out of those frequency components, or the suppressing operation is time-sequentially performed on each frequency component. In other words, there have been problems such as a problem of non-setting of an appropriate notch filter against mechanical resonance containing a plurality of frequency components, thus preventing exertion of an oscillation suppressing effect, and a problem of needing of time for suppressing an oscillation. Further, as means for estimating a frequency, a method through use of a zero-cross cycle, a method based upon a frequency analysis such as FFT, and the like, may also be considered. However, there have been problems such as a problem with the former method in that a stable cycle cannot be obtained in the case of mechanical resonance containing a plurality of frequency components, and a problem with the latter method in that a frequency cannot be accurately estimated unless the number of data to some extent is obtained, and thereby requires time.